Welding an extension on a drill bit.

Stan in Oly, WA

Well-known Member
Does anyone have a suggestion about how to maintain perfect alignment when welding a piece of rod to the end of a drill bit to make an extension? I won't have a problem maintaining the temper of the cutting end of the bit, but my previous attempts to weld any rod-like items together have always produced hit and miss results. I usually don't try it with things where close tolerances matter, but this is a favor for a friend and I'd like to do it right.

Stan
 
You could lay the drill bit and the extension in the valley of a section of small aluminum angle. The length of the angle should be equal to the length of the drill + extension. This should hold them in alignment while you make the initial tack.
 
You can buy drill bits 3-4' long. If you are going to try to make one you could just clamp it to a board until you get one side welded. Once you have that you could roll it over and weld the other side.
 
I've done it a couple ways with success--as mentioned, if the pieces are the same diameter you can put them in a piece of angle (I used steel angle and it worked fine) or I also have clamped the drill bit in my lathe's tail chuck and ran the extension through the headstock. In both cases I've tapered the ends of both pieces first to give the weld a bit more strength.
 
Drill a 1" or larger hole in a board. Clamp rod and drill to board. Weld on top and from the the bottom. Unclamp rotate, reclap and weld again. 4 v blocks would work better. 5he need to be in a v of some sort to keep them straight.
 
Stephen; Your suggestion for how to do the weld is a good one, as are most of the others here so far. Buying a drill bit that's already long enough might be the best answer except that this bit is exotic enough that I haven't seen one like it before, and my friend doesn't remember where he got it or what it's called. At first glance it looks like a forstner bit but it's got three legs with cutting blades on them. End on it looks like the logo of some familiar company, but I can't place it.

Stan
 
Hello Stan in Oly, WA,

I would brace the extension to the bit. Have the pieces in place with a gap between before use adding the brazing rod. If the two pieces turns out a bit off, reheating them at the joint will be easy so you can get them straight,

Guido.
 
I have welded many of them together, I have a jig to hold them, but it's at home and I am traveling. If your extension rod is the same diameter just clamp it in the angle iron jig and weld. If it's not use shims to get it centered. One time we drilled about 2 feet into a 5 inch drive shaft for a paper machine with welded up drill bits, in the middle of the night!
 
So you're using a (basically) 7/8" dia. drill bit? Is it metric?? What's the shank dia. that fits into the drill? Is it round shank or does it have flats for the chuck to grab?

If the drill shank is round AND smaller diameter than the bit, then measure what the shank OD is and write it down. Now find yourself some thick-walled steel tubing that has a matching diameter, and then a short piece of rod that has a matching diameter. The solid rod at one end would go into the drill chuck and into one end of the tubing. The drill bit shank would go into the other end of the tubing. If everything is already a matching size to begin with, then you should have little, if any, wobble. Make whatever length you need....within reason. Just keep in mind that since the drill's flutes will be exceeded, you'll have to remove the bit regularly to clear the cuttings.
 
So you're using a (basically) 7/8" dia. drill bit? Is it metric?? What's the shank dia. that fits into the drill? Is it round shank or does it have flats for the chuck to grab?

If the drill shank is round AND smaller diameter than the bit, then measure what the shank OD is and write it down. Now find yourself some thick-walled steel tubing that has a matching diameter, and then a short piece of rod that has a matching diameter. The solid rod at one end would go into the drill chuck and into one end of the tubing. The drill bit shank would go into the other end of the tubing. If everything is already a matching size to begin with, then you should have little, if any, wobble. Make whatever length you need....within reason. Just keep in mind that since the drill's flutes will be exceeded, you'll have to remove the bit regularly to clear the cuttings.

I do something similar except I drill and ream a hole in the end of a solid rod on my lathe so the drill shank is a nice fit. Then Braze or TIG weld together. If needed, I also would turn the other end down to fit the drill chuck
 
kcm.MN; It's the same basic configuration as a forstner bit, except that it's got three arms holding the three cutters instead of two arms holding two cutters. It would be difficult to explain what it will be used for if the extension I put on it works. That's not really my concern as long as I can make it workable.

Stan
Forstner bit
 
grizz02; I'm not sure why a regular drill bit extension won't work since the diameter of the cutter is 7/8" which I'm pretty sure is larger than the largest diameter on a drill bit extension big enough to hold the approximately 1/4" shaft. My friend told me he has many drill bit extensions and they haven't worked in this application. He's always known what he's talking about before, so I expect that he does this time too. The bit he wants the extension welded onto is similar in shape to a forstner bit.

Stan
forstner bit
 
In building molds and the need for cooling passages at many different depths it is necessary to weld extensions to drill bits that will not cause a bind. Some of our molds take holes 30 or more inches thru. We use a set of V blocks clamped to piece of bar stock.
like these
 
I believe what you are describing is an auger bit. Some of them have three cutters. Depending on what you are doing you might be able to use a 7/8" paddle bit with a extension. They make extension rods that just hold the bit with a couple of set screws. You can even put two or more of these extension rods together. It won't work for an auger though, you would need to weld a rod to it.
a270152.jpg
 
If you have a lathe just go to tsc and buy a 5/8 steel rod. Turn it down to fit the drill except about an inch and a half. Bore that end on the lathe and it will be true. I drill and tap the heavy part to accept 4 allen type set screws. You could weld or braze it just as easy. If it were me and I was going to weld it I would bore a 1/4 through hole in the center so I could weld there on both sides to eliminate the weld distortion on the bit easier.
 
Taper both ends and TIG weld it so the connection is all weld. Don't weld it all in one setting, allow it to cool between passes. That diameter can be done using a piece of angle iron using C clamps and rotating the shaft after the first (small) (welds) cools. Take time and you will have very little wobble. Any wobble can be taken out on some type of anvil.
 
Stan, not 100% accurate but works for me. First spot on the open side then remove and grind weld so if anything its smaller than rod diameter and reclamp at 180 deg. and spot again. Repeat at the other 90 degs.
a270157.jpg

a270158.jpg
 
Stephen; It's not an auger bit. It looks like what you would have if the shaft of the bit started directly behind the black part of the bit in your picture, like a propeller on a shaft.

Stan
 
Jim Rush; What kind of clamp is that holding the bit and the rod? It looks purpose built, but maybe it's some kind of standard clamp and the tightening mechanism is out of sight. Maybe I'm overthinking this but it seems like I might run into a problem getting a C-clamp or bar clamp to tighten against the outside corner of a piece of angle stock, and I'd have to shim out on the rod and bit to have the other jaw of the clamp press them firmly in place.

I'm thinking now that the suggestion of notching a length of 2x4 and putting a large hole under the place the pieces to be welded will join is the method that doesn't require anything I don't already have, and basically accomplishes what your method does with less, but still acceptable, accuracy.

Thanks,

Stan
 
Jim in rush co; Excuse me for getting your name wrong. I'm kind of overwhelmed with half a dozen things going on this morning---each of them needing to be done first.

Stan
 
Hello Stan in Oly, WA,


Is this the bit? Here is another way. Your adapter - extender can be fitted inside the tool end?

Guido.
a270163.jpg

a270164.jpg
 
Stan: I'm betting this clamp is the HF version of what Jim used, though he may have modified his slightly. I bought several of these sets a number of years ago at HF and they have paid for themselves a dozen times over. They don't have the clamping force of a higher-dollar clamp but in most cases I find if I have to clamp them that tight my fit-up needs improving. Also, if they need a bit of Field Expediency for a particular job, it's only 5 bucks to replace if necessary, though I often find the modified ones get used more than the "regular" ones.
HF welding clamp
 
Hi Guido; It's not an auger bit. See my last reply to Stephen Newell at the bottom of this thread---the one I sent at 10:50:26. I think I've received enough good advice about this project that I'm pretty confident that I can do an acceptable job of it. Thanks for your help.

Stan
 
TimV; I have one or two of those with the two flats for jaws, but I don't remember ever seeing the other one before---the one that is for holding pipe or round stock (the bottom one in the ad). It looks like it would be useful.

Stan
 
They are, and not just for pipe. They're equally useful when butt welding flat stock and lots of other uses. Video below is less than a minute long but will give you some ideas.
locking welding clamp
 
You're right, Tim. That looks really useful. I'll get a few the next time I shop at Harbor Freight. I missed their giant three day parking lot sale which ended yesterday. I was kind of kicking myself because their prices were marked down to exactly the same as always, but with a lot more advertising. That's one of the things I like most about Harbor Freight---their sales are like buses; there will be another one just as good if you can wait a few days.

Stan
 
David G; That's a good suggestion. I usually try to step back from a problem and see if there's another way to approach it, as you did here, but it eluded me this time. Thanks.

Stan
 
A hole drilled in the midpoint of that angle would allow you to weld all sides without the weld buildup causing it to "rock".

I use two pieces of angle iron with the outside corner of both pieces rounded. They will lay in a longer piece of angle iron, slightly separated, and allow you to ignore the weld buildup.
 

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